Apparatus for securing an electronic unit to an avionics tray

ABSTRACT

Apparatus for removing and securing a plug-in electronic unit or the like to or from an avionics tray comprises a threaded spindle carrying a transverse pin at one end thereof and having an arrangement of three concentric sleeves located about the spindle. Stop members are provided to limit the movement of the sleeves in both axial directions along the threaded spindle. A rotatable grip is fitted about the innermost of the three concentric sleeves at that end of the sleeve remote from the transverse pin. A ring member is positioned about the middle of the three sleeves and cooperates with an extended flange of the latter to define an annular recess which contains a resilient element. A torque-limiting arrangement is provided between the rotatable grip and a co-operating surface portion of the middle of the three sleeves. The outermost sleeve has, its end closest to the transverse pin, a radial flange which together with said ring member defines an annular recess capable of receiving a hook forming part of the attachment mechanism of an electronic unit. In use, rotation of the rotatable grip allows an electronic unit to be inserted into an avionics tray with a predetermined degree of force, this being adjusted via the torque limiting arrangement. Rotation of the rotatable grip in the opposite sense effects removal of the electronic unit from the avionics tray.

This invention relates to apparatus for securing an electronic unit orthe like to an avionics tray.

Electronic equipment for use in aircraft has been generally standardisedinto set sizes of electronic units. These units are supported onavionics trays which are likewise of standardised sizes.

When an electronic unit is mounted onto an avionics tray, electricalconnections must be made in order to allow the proper functioning of theequipment. Usually, the electronic unit is provided with a bank of pinswhich meet with a corresponding socket provided in or on the avionicstray. Because of the delicacy of the equipment and the need to ensureproper electrical connections, the method of mounting the unit on anavionics tray, and correspondingly of extracting the unit from theavionics tray, assumes an important role. In order to ensure properelectrical connection, an appropriate degree of force is required toinsert the pins into their respective sockets. Too much force, however,could lead to damage to the electronic unit or to the connections, andtherefore the appropriate insertion forces for a particular electronicunit can be defined within a relatively narrow range.

Early avionics equipment hold-downs consisted of a threaded spindlepivoted at one end on a pivot axis transverse to the longitudinal extentof the spindle; the spindle carried a butterfly nut having attachedthereto a taper ring having a taper surface resembling a jaw facing thespindle pivot. By screwing the butterfly nut down towards the pivot, thetaper ring could engage with a projecting hook provided on the front endof the electronics unit. At this stage, little attention was given tothe question of force applied to the electronics unit. An arrangement ofthe kind just described is disclosed in Arinc Specification No. 404relating to air transport equipment cases and racking, which was issuedin May, 1956. Page 53 of the specification (data sheet 9B) states thatcare should be taken in the design of the hold-down screw arrangement inorder to maintain proper relationship of the horizontal force tending tomove the electronic equipment into the electrical connectors and thevertical force holding the equipment down on slide rails which areassociated with the avionics tray.

According to the present invention, there is provided apparatus forremoving and securing a plug-in electronic unit or the like from or toan avionics tray, which apparatus comprises:

(i) a threaded spindle one end of which includes a transverse pin forpivotally mounting the spindle in a retaining member attached to orforming part of the avionics tray such that the spindle can move aboutthe transverse axis of said pin but cannot rotate about its own axis;

(ii) a first sleeve having a first portion relatively remote from thetransverse pin and having a second, internally threaded portion which isthreaded onto the spindle, the internal diameter of the first portionbeing slightly greater than the external diameter of the spindle;

(iii) a first stop member formed in or attached to the end of the firstsleeve nearest to the transverse pin;

(iv) a second stop member arranged to limit the movement of the firstsleeve with respect to the spindle in a direction away from thetransverse pin;

(v) a rotatable grip fitted about that end of the first sleeve remotefrom the transverse pin;

(vi) a second sleeve coaxial with, and positioned around the firstsleeve and having at its end remote from the transverse pin a radialflange including a shoulder facing towards the transverse pin, and anannular recess which co-operates with the rotatable grip and the firstsleeve to define an annular cavity around the first sleeve;

(vii) a torque limiting arrangement positioned in said annular cavityand serving to interconnect the rotating grip and the first sleeve suchthat rotation of the grip in the direction towards the transverse pincauses the first sleeve to move along the threaded portion of thespindle towards the transverse pin so long as the torque between gripand said first sleeve is less than a predetermined value;

(viii) a ring member including (a) a sleeve portion coaxial with andpositioned for sliding movement on the outer surface of the secondsleeve, (b) an internal surface open towards the transverse pin, and (c)a shoulder facing towards, and capable of abutting, the shoulder of thesecond sleeve;

(ix) a third sleeve coaxial with and positioned for relative slidingmovement over that part of the outer surface of the second sleevenearest to the transverse pin, the third sleeve being retained at itsend nearest to the transverse pin by the first stop member and having,at that end, (a) radially inwardly facing abutment which holds the thirdsleeve away from the first sleeve and which defines, in cooperation withthe inner surface of the third sleeve, the outer sleeve of the firstsleeve, and the end of the second sleeve, a sheath-like cavity aroundthe first sleeve, and (b) a radially outwardly extending flange, theother end of said third sleeve being in contact with the radially inwardpart of the taper ring;

(x) a resilient element located in said sheath-like cavity and arrangedso as to tend to urge the second and third sleeves away from one anotherin the axial direction of the spindle;

(xi) a generally cylindrical, elastomeric spacer element held betweenthe radial flange of the second sleeve and that end of the ring memberremote from the transverse pin, the arrangement being such that when thering member and said radial flange move towards each other theirrespective shoulders come into abutment so as to retain the compressedelastomeric spacer element within a cavity defined between the ringmember and said radial flange; and

(xii) means for urging the rotating grip towards the torque limitingarrangement.

The second sleeve may be disposed for sliding movement around the firstsleeve or it may be fixed to the first sleeve.

The torque limiting arrangement preferably comprises a plurality of ballbearings held against the surface of a drive plate, which surface isformed with a number of indents corresponding to the number of ballbearings. Each of the indents can conveniently be generally "L"-shapedin section. The drive plate is preferably keyed to the spindle.

The means for urging the rotating grip towards the torque limitingarrangement preferably comprises a pack of disc springs such asBelleville washers housed in an annular cavity formed between the outerwall portion of the rotating grip and the outer surface of the firstsleeve, the disc springs being urged towards an inner face of therotating grip through the action of an adjustable screw arrangement,e.g. in the form of an adjustment disc threadedly engaged with that endof the first sleeve remote from the transverse pin. By adjusting such adisc, the torque at which the torque limiting arrangement will slip canbe varied.

It is preferred that the outer surface of the rotating grip be formed ofrubber and be shaped so as to facilitate manual operation thereof.

It is also preferred that the outer surface of the rotating grip or atleast a portion thereof be colour coded, a specific colour correspondingto the predetermined value of the torque at which the torque limitingarrangement will slip.

The transverse pin can be mounted in a slot which is inclined withrespect to the support surface of the avionics tray, that end of theslot furthest from the rotating grip being slightly higher than theother end of the slot, when the avionics tray is in a horizontalposition. Alternatively, the spindle may be provided with a pair ofparallel and spaced transverse pins which ride over correspondingsurfaces of an inclined ramp.

For a better understanding of the invention, and to show how the samemay be carried into effect, reference will now be made, by way ofexample, to the accompanying drawings, in which:

FIG. 1 is a side elevational view of apparatus in accordance with thepresent invention;

FIG. 2 is a partial cross-sectional view along the lines A--A of FIG. 1;

FIG. 3 is a cross-sectional view similar to that of FIG. 2, but showingthe apparatus in a first, operative configuration;

FIG. 4, is similar to FIG. 2, but with the apparatus in a second,operative configuration;

FIG. 5 is a view of an alternative form of retaining device for theapparatus of FIG. 1; and

FIG. 6 is a sectional view, on an enlarged scale, of part of theapparatus shown in FIGS. 1 and 2.

Referring now to FIGS. 1 and 2 of the drawings, the apparatus comprisesa threaded spindle 1 one end of which includes a transverse pin 2 forpivotally mounting the spindle in a retaining member attached to, orforming part of, an avionics tray (not shown). In use, this pivotalmounting will be such that the spindle can move about the transverseaxis of pin 2, while being unable to rotate about its own longitudinalaxis. A first sleeve 3 includes a first portion 4 remote from pin 2 anda second, internally threaded portion 5 which is screw-threaded onto thespindle 1. The internal diameter of portion 4 of sleeve 3 is slightlygreater than the external diameter of spindle 1. The end of sleeve 3closest to transverse pin 2 flares outwardly to constitute a first stopmember 6. A second stop member 7, in this embodiment in the form of acap threaded internally into spindle 1, is arranged to limit themovement of the first sleeve 3 with respect to spindle 1 in thedirection away from transverse pin 2.

A rotatable grip 8 is fitted about the end of first sleeve 3 remote fromtransverse pin 2. The grip comprises a colour-coded rubber grip surface27 secured to the periphery of a cylindrical section 29. Cylindricalsection 29 has, at its right-hand end as seen in FIG. 2, a recess inwhich are disposed a pack of disc springs (e.g. Belleville washers) 25.These are held in position by an adjustable disc 24 which is threadedonto the end of the first sleeve 3 furthest from pin 2. This disc 24urges the disc springs 25 against inner surface 30 of the rotating grip8.

A second sleeve 9 is coaxial with and positioned around the first sleeve3. Sleeve 9 is preferably secured to the first sleeve 3. A radial flange10 is formed at the end of sleeve 9 remote from pin 2. Flange 10includes a shoulder 11 facing towards the pin 2 and an annular recess 12which co-operates with the rotatable grip 8 and the first sleeve 3 todefine an annular cavity around the first sleeve. In this cavity atorque limiting arrangement 13 is positioned. This comprises a driveplate 26 which is keyed to sleeve 3 and a plurality of ball bearings 31.Cavity 13 also includes a spacer member 32. A partial sectional viewalong lines B--B is shown in FIG. 6. As can be seen from this Figure,the drive plate 26 is associated with four ball bearings 31 each ofwhich is seated in an indent 33. Each indent is "L"-shaped, having arelatively shallow sloping surface 34 and a relatively steep slopingsurface 35. These two surfaces lie in planes which are 90 degrees apart.As seen from FIG. 6, the keying of drive plate 26 is effected throughflats 36 formed in sleeve 3.

The torque limiting arrangement 13 is arranged such that rotation of thegrip 8 in the direction causing sleeve 3 to move towards the transversepin 2 continues so long as the torque between grip 8 and the sleeve 3 isless than a predetermined value. By adjusting screw 24, thispredetermined torque value can be set appropriately.

Annular ring 14 is mounted for sliding movement on the outer surface ofthe second sleeve 9. The ring 14 includes a sleeve portion 15 coaxialwith the second sleeve 9, and an internal surface 16 open towards thetransverse pin 2. A shoulder 23 is also provided on the ring, thisshoulder facing towards, and being capable of abutting, the shoulder 11of sleeve 9. A generally cylindrical, elastomeric spacer element 22 isheld captive between the radial flange 10 of second sleeve 9 and theright-facing end of the ring 14. When the ring 14 and flange 10 movetowards each other, their respective shoulders 11 and 23 come intoabutment so as to retain the compressed elastomeric spacer element 22within the cavity formed between members 14 and 10.

A third sleeve 17 is coaxial with and positioned for relative slidingmovement over that part of the outer surface of second sleeve 9 nearestto the transverse pin 2. Sleeve 17 is retained at the left hand end asseen in FIG. 2 by stop member 6. At the same end, the third sleeve 17has a radially inwardly facing abutment 18 which holds the third sleeve17 away from the first sleeve 3. Abutment 18 also defines, inco-operation with the inner surface of the third sleeve 17, the outersurface of the first sleeve 3 and the end of the second sleeve 9, asheath-like cavity 21 around first sleeve 3. A resilient element 20 islocated in cavity 21 and is arranged so as to tend to urge the thirdsleeve 17 away from second sleeve 9 in the axial direction of thespindle 1. Third sleeve 17 also includes a radially outwardly extendingflange 19 at the end adjacent to transverse pin 2. The other end ofsleeve 17 is in contact with the radially inward part of the ring 14.

The operation of the apparatus illustrated in FIGS. 1 and 2 will now bedescribed with reference to FIGS. 2, 3, 4 and 5.

As shown in FIGS. 3 and 4, the transverse pin 2 is located in a slot 40formed in a retaining member 41. The retaining member 41 is secured tothe lower part 42 of an avionics rack (not shown). The avionics racksupports an electronic unit which includes a front plate 43 havingattached thereto a generally L-shaped hook 44. Front plate 43 includes alower portion 45 which extends somewhat below the generally flat, bottomsurface of the electronics unit which is supported on rack 42.

In FIG. 3, the apparatus of this invention is shown in the configurationapplicable to its use in extracting the electronics unit from the rackor tray on which it is supported. In this configuration, the lower part45 of front plate 43 and the toe of hook 44 are engaged between flanges19 and 14 of the apparatus. Rotating grip 8 is rotated in a directionsuch as to move first sleeve 3 towards the right-hand end of spindle 1as shown in the drawing. Torque is transferred through the arrangement13 to plate 26, which as shown in FIG. 6 is keyed onto sleeve 3. Secondsleeve 9 is fixed with respect to first sleeve 3, and third sleeve 17 isheld in position between taper ring 14 and the enlarged end portion 6 offirst sleeve 3, which acts as a retaining member. The jaw-like flange 19of third sleeve 17 is thus caused to exert force on the rear portion 45of front plate 43, thus pulling the electronics unit to the right asshown in FIG. 3, thereby extracting the unit from its support tray andsimultaneously effecting disconnection of the electronic connectionsassociated with the unit. During an extraction operation, the transversepin 2 is held in slot 40 in the position illustrated in FIG. 3. The slot40 is generally similar in function to that described and illustrated inU.S. Pat. No. 3,147,005.

When the apparatus of the invention is used to insert an electronicsunit, the configuration shown in FIG. 4 is adopted. Rotating grip 8 isturned in the direction causing sleeve 3 to move to the left as shown inthe drawing, the overall effect being that the inward facing surface 16of taper ring 14 pushes against the toe of hook 44, thus moving theelectronics unit to the left and effecting the necessary electricalconnections. As the apparatus moves from the configuration shown in FIG.3 to that shown in FIG. 4, rotation of grip 8 initially brings the toeof hook 44 into engagement with the surface 16 of ring 14. As the gripis tightened further, shoulders 11 and 23 are brought together againstthe force of the elastomeric coupling element 22. Eventually, shoulders11 and 23 meet to give the arrangement shown in FIG. 4, where elements22 is trapped in the cavity defined by co-operating surfaces of taperring 14 and flange cam. Further rotation of the grip 8 acts to move theelectronics unit to the left, as indicated above.

The torque limiting arrangement 13 is effective during the insertionmode. By adjusting the disc springs 25 via threaded disc 24, thelimiting torque can be varied according to that desired for anyparticular application. When the electronics unit is fully seated on theavionics tray and the electronic connections have been effected, furtherrotation of rotating grip 8 will have no effect other than to cause thetorque limiting arrangement 13 to slip. In the embodiment illustrated,the torque limiting arrangement 13 is effective only in the insertionmode: in other words, the arrangement 13 acts as a direct drive whenrotating grip 8 is rotated in the sense required to extract theelectronics unit from the rack, i.e. as described above with referenceto FIG. 3.

FIG. 5 shows an alternative mounting arrangement for apparatus of thisinvention. Instead of a slot 40, the mounting means 41 includes aninclined ramp 46 the opposite surfaces of which co-operate with twotransverse pins 2a and 2b respectively.

What is claimed is:
 1. Apparatus for removing and securing a plug-inelectronic unit .Iadd.or the like .Iaddend.from or to an avionics tray,which apparatus comprises(i) a threaded spindle one end of whichincludes a transverse pin for pivotally mounting the spindle in aretaining member attached to or forming part of the avionics tray suchthat the spindle can move about the transverse axis of said pin butcannot rotate about its own axis; (ii) a first sleeve having a firstportion relatively remote from the transverse pin and having a second,internally threaded portion which is threaded onto the spindle, theinternal diameter of the first portion being slightly greater than theexternal diameter of the spindle; (iii) a first stop member formed in orattached to the end of the first sleeve nearest to the transverse pin;(iv) a second stop member arranged to limit the movement of the firstsleeve with respect to the spindle in a direction away from thetransverse pin; (v) a rotatable grip fitted about that end of the firstsleeve remote from the transverse pin; (vi) a second sleeve coaxialwith, and positioned around the first sleeve and having at its endremote from the transverse pin a radial flange including a shoulderfacing towards the transverse pin, and an annular recess whichcooperates with the rotatable grip and the first sleeve to define anannular cavity around the first sleeve; (vii) a torque limitingarrangement positioned in said annular cavity and serving tointerconnect the rotating grip and the first sleeve such that rotationof the grip in the direction towards the transverse pin causes the firstsleeve to move along the threaded portion of the spindle towards thetransverse pin so long as the torque between grip and said first sleeveis less than a predetermined value; (viii) a ring member including (a) asleeve portion coaxial with and positioned for sliding movement on theouter surface of the second sleeve, (b) an internal surface open towardsthe transverse pin, and (c) a shoulder facing inwards, and capable ofabutting, the shoulder of the second sleeve; (ix) a third sleeve coaxialwith and positioned for relative sliding movement over that part of theouter surface of the second sleeve nearest to the transverse pin, thethird sleeve being retained at its end nearest to the transverse pin bythe first stop member and having, at that end, (a) a radially inwardlyfacing abutment which holds the third sleeve away from the first sleeveand which defines in cooperation with the inner surface of the thirdsleeve the outer surface of the first sleeve and the end of the secondsleeve, a sheath like cavity around the first sleeve, and (b) a radiallyoutwardly extending flange, the other end of said third sleeve being incontact with the radially inward part of the taper ring; (x) a resilientelement located in said sheath-like cavity and arranged so as to tend tourge the second and third sleeves away from one another in the axialdirection of the spindle; (xi) a generally cylindrical, elastomericspacer element held between the radial flange of the second sleeve andthat end of the ring member remote from the transverse pin, thearrangement being such that when the ring member and said radial flangemove towards each other, their respective shoulders come into abutmentso as to retain the compressed elastomeric spacer element within acavity defined between the ring member and said radial flange; and (xii)means for urging the rotating grip towards the torque limitingarrangement.
 2. Apparatus as claimed in claim 1, wherein said secondsleeve is fixed to said first sleeve.
 3. Apparatus as claimed in claim1, wherein said second sleeve is free to slide over said first sleeve.4. Apparatus as claimed in claim 1, wherein said torque limitingarrangement comprises a plurality of ball bearings held against thesurface of a drive plate, which surface is formed with a number ofindents.
 5. Apparatus as claimed in claim 4, wherein each of saidindents is generally "L"-shaped in section.
 6. Apparatus as claimed inclaim 4 .Iadd.or 5.Iaddend., wherein said drive plate is keyed to thespindle.
 7. Apparatus as claimed in claim 1, wherein said torquelimiting arrangement comprises a pack of disc springs housed in anannular cavity formed between an outer wall portion of said rotatinggrip and the outer surface of said first sleeve, the disc springs beingurged towards an inner face of the rotating grip through the action ofan adjustable screw arrangement.
 8. Apparatus as claimed in claim 1,wherein the rotating grip or at least an outer surface portion thereofis colour-coded to indicate the maximum limiting torque to which thetorque limiting arrangement can be set.
 9. Apparatus as claimed in claim5, wherein said drive plate is keyed to the spindle.